Item Builds

This build is what I use most of the times in general. Sometimes you will need to differ abit with the build, because of different opponents.. If you think you wont need to move fast around the map, you can choose either mercury treads or ninja tabi. If your goal is to get abit more health and ad/armor pen, you can buy Black Cleaver instead of Last Whisper. I normally go for Last Whisper, because its cheaper and as a jungler you cant always purschase the expensive items.
When the enemy team doesn't have any sources of magic damage and your goal is to build more armor.. you can buy sunfire+ ROmen's or ROmen's + thornmail.
For the late game part, you can sell the elders lizzard item and buy hydra if you want to make more damage or buy Guardians Angel if you need to survive more. I usually keep my ruby sight stone for all the match, because its a awesome item for lee (Buy sight stone and only upgrade for ruby as the last item).
Choices that you can prefer:
-spirit visage insted of banshee's Veil
-guardian angel insted of sight stone (more late game if you want more resists)
-maw of malmortius insted of banshee's Veil
-Black cleaver insted of last whisper (as i said before)

Skill Order

Some advices

The most important thing about Lee Sin is: You have to buy wards. ("WARDS SAVES LIVES")
You use smite when you are using the second "W" to regen some heath.
try to use your passive as much as you can, as it helps you jungle way faster. In order to do so, use a skill then two basic attack and use the second part of the skill. Pretty straight forward.
If you feel confortable doing counter jungle.. Lee is one of the best champions to do that. For example, when I play on the blue side I usually (after taking my red) clean wraiths and run for the enemy red to steal it and kill the other jungle (Getting the timers of all buffs and taking control of the game with some wards e.t.c.)
Be careful if their teammates get to help him and they take you down.. because you will get be in a bad position, considering their jungle will be on the lead and so their team.